It is desirable to detect flames for early alarming of a fire. A typical method is that of triple-infrared (IR) which involves three detectors: for example, one tuned to the 4.4 μm carbon dioxide emission band line, that is formed when hydrocarbons burn, and the other two tuned to off-band lines, to discriminate between a flame and hot objects. These sensors typically look at a 90 degree field of view, but are not capable of discerning individual sources of radiation within that field of view.
Another approach is to use an imager so that the camera can better discriminate between a flame and hot objects within the field of view. An imager makes it possible to see flames even when there are other hot objects in the field of view that are in different locations.
However, there are several potential problems with such a solution. For example, in some instances, the optics may get coated or an object may be in the way of the field of view. This can impair the viewing of a flame and/or its identification.
It is also desirable to look at objects in the field of view and discern whether these objects are emitted at 4.4 μm which may be an indicator of a flame, rather than just a hot item in the field of view. To do this currently requires the use of a filter wheel, capturing separate images at the desirable spectral bands, but the moving parts associated with such filters can lead to failure.